| Coordinated Multipoint(CoMP)is a key technique to improve cell average and edge throughput in inter-cell interference scenarios in mobile communication system.It can exploit the coordination of base stations and avoid or even utilize interference dynamically.The up-link CoMP joint reception with distributed antenna system(DAS)architecture can exploit the diversity gain and achieve the best performance gain.However,CoMP joint reception requires high capacity backhaul between base stations and central unit.If the capacity is restricted,the performance is also restricted.As the current techniques for up-link CoMP joint reception have some shortages,a novel technique is proposed in this paper which use integer forcing(IF)into CoMP.Compute-and-Forward(Co F)is one of the current techniques.It achieves good performance under the restriction of low backhaul capacity between base stations and central unit.However,it cannot be used in a multi-antenna system.This paper inherits the idea of CoF and extends it to the CoMP system with multi-antenna base stations.A CoMP system using integer forcing(CoMP-IF)is proposed,including the system architecture,signal processing flow and a coefficient vector selecting algorithm based on Gauss-Jordan elimination.This system can exploit the diversity gain of CoMP channel with low backhaul capacity,as it transmits nested lattice codewords in backhaul.However,this system has some defects.Firstly,it cannot be used in the scenario with more users than base stations.Secondly,it can’t work sometimes because the system can’t solve the linear equations.In order to solve the defects,an improved CoMP-IF system is proposed.By setting the parameter of coefficient vector number dynamically and drawing into control information between central unit and base stations,the system can keep the system in line and improve the performance obviously.By simulating,it’s obvious that the proposed CoMP-IF system achieves higher performance gain than current techniques under backhaul capacity restriction.The largest transmission rate of CoMP-IF system depends on transmission rate under backhaul capacity restriction.By simulating,it’s obvious that with the increasing of interference factor,SNR and antennas number,the largest transmission rate will increase.This means the CoMP-IF system is sufficient to be deployed in typical CoMP scenario with high interference,high antennas number,low backhaul capacity restriction and more users than base stations.CoMP-IF system can increase performance under backhaul capacity restrictionat cost of system complexity increase.In some CoMP system,the computation resource is restricted but the performance requirement is not high.The paper proposes that lattice reduction algorithm can be used instead of SMP algorithm to reduce system complexity significantly at the cost of acceptable performance degradation. |
